Recently, from the viewpoint of energy saving, high-density housing has been increasing for preventing energy loss. On the other hand, for improved performance of air-conditioning apparatus and/or for security reasons, keeping the windows closed virtually at all times has become a common lifestyle choice.
The above living conditions contribute to occurrence of so-called house dust and thus air contamination in the living space becomes an issue. Furthermore, there is a risk of chemicals such as formaldehyde being released from building material and furniture and staying in the living space, which causes the occupants impaired health.
In view of the above problems, in Japan, the revised Building Standard Law, effected as of Jul. 1, 2003, requires a new or renovated building to have 24-hour ventilation equipment, more specifically equipment capable of ventilation 0.5 times/h or more often.
As a ventilation technique in conformity to the above law, for example, Patent Literature 1 (Unexamined Japanese Patent Application Kokai Publication No. 2005-337647) discloses a house equipment control device (home server) controlling an air-conditioning apparatus and/or ventilation equipment having the function of air-purification installed in a living space and ventilating the living space. This home server is connected to a sensor detecting chemicals and the like and as the sensor detects sick building substances, orders the air-conditioning apparatus or the like to conduct ventilation. Furthermore, this home server orders the air-conditioning apparatus or the like to conduct ventilation every two hours (0.5 times/h) even if the sensor detects no sick building substances.
In comparison with manual operation by the occupants, automatic ventilation of the living space at least every two hours such as the technique described in the Patent Literature 1 causes the ventilation apparatus such as ventilation fans to operate more frequently and increases the power consumption. Then, efficient ventilation is required as an energy saving measure. The Patent Literature 1 has no description of efficient ventilation. Thus, actually, there is a demand for a new technique for efficient ventilation of a living space.